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Weathering and Soil Formation Ayers Rock… Another View Coach Holmes indicator for, “How far out in the boonies are we?” Distance from civilization. Approximately how far away from Ayers Rock is the closest McDonalds restaurant? 465 km (289 miles). The closest McDonalds is in Alice Springs. 22 km to Yulara then another 443 km to Alice Springs Essential Question: NCSCOS: EEn.2.1.3 Explain how natural actions such as weathering, erosion(wind, water and gravity), and soil formation affect the Earth’s surface. E.Q. - What are the mechanisms of weathering Objectives and Goals Recall that soil is the result of weathering of rocks and includes weathered particles: sand, silt and clay. Explain differences in chemical and physical weathering how weathering rates are affected by a variety of factors including climate, topography and rock composition. Writing: In your journals: Give your definition of weathering. Part I Weathering The breaking down of rocks and other materials on the Earth’s surface is called weathering. A slow, continuous process, it affects all substances exposed to the atmosphere. Types of Weathering •Rocks on the Earth’s surface are broken down by two types of weathering: •mechanical and chemical. Mechanical Weathering When the forces of weathering break rocks into smaller pieces but do not change the chemical makeup of the rocks, the process is called mechanical weathering. During mechanical weathering, rocks are broken into different shapes and smaller pieces. At the beginning the edges are jagged, as weathering continues, they become round. Causes of Mechanical Weathering Must involve motion or movement Temperature / Exfoliation Frost action / Ice wedging Organic activity / Root Pry Gravity / Rolling down hill Abrasion / Sand blasting Glacier / Till Temperature Rocks can be broken apart by changes in temperature. As rocks are heat up in the sun during the day, the outside of the rock expands. The inside of the rocks remain cool and do not expand. When the air temperature drops at night, the outside of the rock cools and contracts. This continuing cycle causes particles to break off. This is called exfoliation. Rock Exfoliates Study the figure and answer the questions below in your notebook. a Are the changes in temperature gradual or rapid? b In which regions do these fluctuating temperatures often occur? c Where are the points of weakness in the rock? Frost Action Unlike most liquids, water expands when it freezes. The repeated freezing and melting of water, called frost action, is another cause of mechanical weathering. When water freezes in cracks in the rocks, it expands, making the crack larger.In time, this causes the rock to break into pieces. Ice Wedging / Frost Action Study figure and answer the questions below in your notebook a Where is the rainwater going? b What happens when temperatures fall below 0°C? c Why has the crack widened? d What effect will this have on the rock? e Which process does this flow chart illustrate? Organic Activity Plants and animals can cause mechanical weathering. The roots of plants sometimes loosens rock material. A plant growing in a crack can make the crack larger as the root spread out. This is known as root-pry. It is organic since this activity is caused by living things. Study the figure and answer the questions below in your notebook. a What happens to the crack as the roots get bigger? b What kind of weathering is this? c What kind of weathering does this process cause? d The decaying tree will provide… Gravity Gravity is another agent of mechanical weathering. Sometimes gravity pulls loosened rocks down mountain cliffs in a landslide. A landslide is a large movement of loose rocks and soil, know as MASS MOVEMENT. As the rocks fall, they collide with one another and break into smaller pieces. Falling rocks usually occur in areas where a road has been cut through, leaving cliffs on both sides. Abrasion Wind-blown sand causes mechanical weathering . Abrasion is the wearing away of rocks by solid particles carried by wind, water or other forces. In desert regions or at the beach, the wind easily picks up and moves sand. The sharp edges of the sand particles scrape off pieces of exposed rocks. Running water also carries loose rocks which scrape against each other and break. Sandblasting Art http://www.youtube.com/watch?v=apjYHZKZV6k&safety_mode=true&persist_safety_mode=1 Chemical Weathering When the chemical makeup of the rocks is changed it is called chemical weathering. During chemical weathering, changes occur in the mineral composition of rocks. Minerals can be added, removed or broken down (decomposed). Many substances react chemically with rocks to break them down. Types of Chemical Weathering The chemical composition must be changed Water /dissolving Oxidation / Rusting Carbonation / Acid Rain weak Sulfuric acid / Acid Rain strong Plant acids / Mosses and lichens Water Most chemical weathering is caused by water and carbon dioxide. Water can dissolve most of the mineral that hold rocks together. Rocks that dissolve in water are said to be soluble. Water can form acids when it mixes with certain gases in the atmosphere to speed up the decomposition of rocks. Water can also combine with a mineral to form a new mineral. Evaporites Our State (Magazine) Linville Caverns Video https://www.youtube.com/watch?v=242YYeGdid4 Oxidation Chemical weathering is also caused by oxidation. Oxidation is the process in which oxygen chemically combines with another substance. The result of oxidation is the formation of an entirely different substance. Iron in rocks combines with oxygen in the air to form iron oxide, or rust. Carbonation When carbon dioxide dissolves in water, a weak acid called carbonic acid is formed. When carbonic acid reacts chemically with other substance, the process of carbonation occurs. In nature, carbonic acid is formed when carbon dioxide in the air dissolves in rain. This acid rain falls to the ground and sinks into the soil. It decomposes feldspar and limestone. Study the figure and answer the questions below in your notebook. a What kind of weathering is this? b How does this kind of weathering affect the rock? c Which climates speed up this kind of weathering? Sulfuric Acid The air in certain areas is polluted with sulfur oxides. Sulfur oxides are a byproduct of the burning of coal as a source of energy. These compounds dissolve in rainwater to form sulfuric acid. Rain that contains sulfuric acid is one type of acid rain. It is much stronger than carbonic acid. Sulfuric acid corrodes rocks, metals and other materials quickly. Plant Acids Plants produce weak acids that dissolve certain minerals in rocks. Mosses and lichens produce weak acids that dissolve some of the minerals in the rocks they grow on in areas of PERMAFROST / Polar Climates. Gradually the rocks break into smaller pieces. They are important in the formation of soil. Rate of Weathering The composition of the rock The amount of time that the rock is exposed on the Earth’s surface The amount of exposed surface on a rock Climate Relief / Topography (Height) Rate of Getting Wet Check your understanding of weathering rates. With a partner list five different ways that your clothes become saturated with rain more and/or faster. Then compare that list with your notes on the rates of weathering Rate of Weathering Graph Composition of Rocks Two different types of rocks in the same climate can weather differently, depending on the minerals that make up each rock type. If a rock resist weathering, the rock is called a STABLE ROCK. The stability of a rock can vary depending on the climate in which the rock is found. Limestone is stable in a dry climate but not in a wet climate. Amount of Time of Exposure The amount of time that rock is exposed on the Earth’s surface also affects its rate of weathering. A very old rock that has not been exposed to the forces of weathering can remain almost unchanged. If a newly formed rock is deposited on the Earth’s surface it will begin to weather right away. Which Is Older???? Vs. The Amount of Exposed Surface The amount of exposed surface area on a rock also affects its rate of weathering. As rocks are broken down into many small pieces, more rock surfaces are exposed and more weathering takes place. In rocks that contain many joints or cracks, various chemicals easily come into contact with the rock surfaces and break them down. Which Dome is more exposed??? Vs. Chimney Tops… G.S.M.N.P. Climate Cold and/or dry climates favor physical weathering. Arctic/Polar Warm and wet climates favor chemical weathering. Tropical Frost action works best in areas where the temperature fluctuates wildly. Temperate Climates Part 2 Part II Erosion and Deposition Essential Question: Compare erosion by water, wind, ice, and gravity and the effect on various landforms What Caused This? What is Erosion? Erosion – the moving of rock material from one place to a new location For erosion to occur three processes must take place: detachment of particles, lifting them, and transporting them Many agents of erosion - flowing water, moving ice, waves, gravity, or wind Sand, silt and clay consists of small pieces of rock that have been weathered from a parent rock, eroded, and deposited somewhere else What Is Wind Erosion? Wind - responsible for wearing away rocks and creating great deserts like the Sahara Desert and Gobi Most effective in moving loose material Two main effects: (1) Wind causes small particles to be lifted and moved away. (2) Suspended particles may impact on solid objects causing weathering by abrasion (rubbing/blasting). Occurs in areas where there is not enough rainfall to support vegetation What Is Water Erosion? Water - most influential force in erosion Ability to move materials from one location to another over long distances The faster water moves in streams the larger objects it can pick up and transport. Known as STREAM LOAD Responsible for wearing away of rocks in rivers, lakes, and the oceans What Is Wave Erosion? Waves - relentless pounding Erodes the softer, weaker parts of the rock first, leaving harder, more resistant rock behind Can take over 100 years to erode a rock to sand Energy of waves along with the chemical content of the water erodes the rock off the coastline What Is Gravitational Erosion? Mass movement - downward movement of rock and sediments, mainly due to the force of gravity. Moves material from higher elevations to lower elevations where streams and glaciers can pick up the material and move it to lower elevations Process is occurring continuously on all slopes, some act very slowly while others occur very suddenly until equilibrium is reached What Is Glacial Erosion? Ice - moves and carries rocks, grinding the rocks beneath the glacier Weathering Abrasion cuts into the rock under the glacier, smoothing and polishing the rock surface With the same glacial process material is transported to new locations. HOMES ??? What is Deposition? Deposition - laying down of sediment that has been eroded/transported by a medium such as wind, water, waves, gravity or ice Process of erosion stops when the moving particles fall out of the transporting medium and settle on a surface. This settling of eroded material into a new location is called deposition. Obstacles, whether natural or man-made, will often decide where the deposition occurs and the nature of the feature formed. What’s the Difference? WEATHERING - think weather wearing rock down EROSION - think of a road and traveling DEPOSITION – think of depositing money in a bank Part III Soils “What is Soil ?” What is Soil? Soil - Soil is a natural body comprised of solids (weathered minerals, rock and decaying organic matter called humus), liquid (water), and gases (air) that occurs on the land surface, occupies space, and is characterized by horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment. What is Dirt??? Often referred to mistakenly as soil. Dirt is actually unclean matter, especially when it is in contact with a person's clothes, skin or possessions when they are said to become dirty. Common types of dirt include mud, dust and, yes, soil itself. Any unclean substance, such as mud, dust, excrement, etc.; filth What’s the difference between soil and dirt? Dirt is what you find under your fingernails. Soil is what you find under your feet. Think of soil as a thin living skin that covers the land. It goes down into the ground just a short way. Even the most fertile topsoil is only a foot or so deep. Soil is more than rock particles. It includes all the living things and the materials they make or change. Soil Formation The weathering of rocks on the Earth’s surface results in the formation of soil. Soil is formed when rocks are continuously broken down by weathering. As rocks weather, they break into smaller pieces. These pieces are broken down into even smaller pieces to form soil. Importance of Soil The formation of soil is extremely important to most living organisms. Plants depend on soil as source of food. Soil supplies plants with minerals and water needed for growth. Animals depend indirectly on soil since they eat plants and other animals that eat plants. Residual Soil; Lives at Home Sometimes soil remains on top of its parent rock, or the rock from which it was formed. This is called residual soil. Residual soil has a composition similar to that of the parent rock it covers. Transported Soil; Erosion Some soil is removed from the parent rock by water, wind, glaciers and waves. Soil that is moved away from its place of origin is called transported soil. Transported soil can be very different in composition from the rock it covers. Bedrock The layer of rock beneath the soil is called bedrock. Also Known as Parent Rock Decay Certain bacteria in the soil cause the decay of dead plants and animals. This decaying material is called humus. Humus is a dark-colored material that is important for the growth of plants. Some of the chemicals produced during the process of decay speed up the breakdown of rocks into soil. Acids Living Things Living things such as moles, earthworms, ants and beetles help to break apart large pieces of soil as they burrow through the ground. The burrows allow water to move rapidly through the soil. The water speeds up the weathering of the underlying rock. Soil Composition Pieces of weathered rock and organic material, or humus, are the two main ingredients of soil. Organic materials is material that was once living or was formed by the activity of living organisms. Rock particles form more than 80% of soil. Air and water are also present in soil. Minerals in Soil Clay and quartz are the most abundant minerals in soil. Because they are stable, they exist in the greatest quantities. Potassium, phosphorus and the nitrogen compounds called nitrates are important chemicals in soil. They are vital to plant growth. Pore Spaces Air and water fill the spaces between soil particles. These are called pore spaces. Plants and animals use the water and air in these spaces, as well as the minerals dissolved in water. Pore spaces provide needed oxygen for healthy plant root growth. Different Compositions of Soil The composition of soil varies from place to place. The type of rock broken down by weathering determines the kinds of minerals in the soil. The type of weathering also affects the composition of soil. Mechanical weathering produces soil with a composition similar to the rock being weathered. Chemical weathering produces soil with a different composition. Soil Texture The type of weathering also affects soil texture. Texture refers to the size of the individual soil particles. Soil particles vary from very small to large. Both mechanical and chemical weathering first breaks rocks into gravel (2-64mm) and then in sand (less than 2mm) and then into silt and finally clay. Soil Horizons As soil forms, it develops separate soil layers called horizons. Each soil horizon is different. A cross section of the soil horizons is called soil profile. A soil profile shows the different layers of soil. Evolution of Soil Horizons Topsoil; Root Zone Parent Rock New Horizon Classification Mature Soil Soil that has developed three layers is called mature soil. It takes thousands of years and the proper conditions for soil to develop three layers. The uppermost layer of mature soil is called the A horizon. The A horizon is a dark-colored soil layer in which much activity by living organisms takes place. Bacteria, earthworms and beetles help the decay. O (Organic) Horizon This is the organic debris that has recently accumulated on the surface of the soil. It has begun to decompose. A Horizon The soil in the A horizon is called topsoil. Topsoil consists mostly of humus and other organic materials. Humus supplies minerals essential for plant growth. Humus is spongy and stores water. It also contains pore space for air and water. Topsoil is the most fertile part of the soil. E (Eluviation) Horizon This eluviation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation). Virgin Soil Soil that has little or no humus/organic mater incorporated. “B” horizon and below Soil that is as yet undeveloped Soil that has not been cultivated before Virgin soil, when compact and of considerable depth, is a good material to build on, providing the structure is not an extremely lofty or heavy one. B Horizon Water that soaks into the ground washes some minerals from the A horizon into the second layer of soil, or the B horizon. This process is called leaching. The B horizon is just below the A horizon. The B horizon is also made of clay and some humus. The soil in the B horizon is called subsoil. Subsoil is formed very slowly. C Horizon The third layer of soil is called the C horizon. The C horizon consists of partly weathered parent rock. The C horizon extends down to the top of the un-weathered parent rock. The composition of the soil in the C horizon is similar to that of the parent rock. What are the differences between eluviation and illuviation? Eluviation is the leaching down or movement of the particles (such as minerals and organic matter) into lower soil horizons. While, Illuviation is the accumulation of those particles in the lower soil horizons. R(rock) Horizon Solid un-weathered bedrock. Referred to Parent Rock. It is either… Permeable – allowing most substance to pass or flow in and out Semipermeable - allowing some substances to pass Impermeable or Nonpermeable – materials cannot pass through Immature Soil In some places, the upper layers of soil are removed and the rocks below the soil are exposed. The weathering process then forms new soil from the exposed rocks. This recently formed soil is immature because there has not been enough time for all three soil layers to form. The soil in the northern regions where glacial erosion has taken place, is immature soil. Formation of Soil There are several factors that determine whether three layers of soil will form. Time Climate Type of rock / Parent Rock Surface features of the region Time Time is one of the most important factors in soil formation. The longer a rock is exposed to the forces of weathering, the more it is broken down. Mature soil is formed if all three layers have had time to develop. Climate Climate is another important factor in the formation of soil. In areas with heavy rainfall and warm temperatures, weathering takes place more rapidly. Heavy rainfall may wash much of the topsoil away. Since Organisms are more plentiful these areas, the soil is quickly replaced. They speed up the chemical and mechanical weathering of rocks. Type of Rock The type of rock in an area also affects soil formation. Some rocks do not weather as rapidly as other do. Rocks that do not break down easily do not form soil rapidly. In some climates it takes along time for granite to break down. So soil formation from granite is slow. But sandstone breaks easily and forms soil quickly. Surface Features of Region The surface features of the region also determine the speed at which soil is formed. On very steep slopes, rainwater running off the land erodes the soil and exposes rock to weathering. Four Soil Formation Processes Genesis These processes of soil genesis, operating under the influence of environmental factors, give us a logical framework for understanding the relationships between particular soils and the landscapes and ecosystems in which they function. This approach is known as internal process modeling. In analyzing these relationships for a given site, ask yourself: Ask yourself… What are the materials being added to this soil? What transformations and translocations are taking place in this profile? What materials are being removed? How do climate, organisms, topography, and parent material affect these processes over time?